(1) Field of the Invention
The present invention generally relates to acoustic systems and more particularly to underwater sound transmitting or receiving systems requiring the unique property of having a directional constant beamwidth diffraction pattern over a wide band of frequencies either with or without scanning. The invention also has use in the electromagnetic area.
(2) Description of the Prior Art
One acoustic system for providing a directional constant beamwidth diffraction pattern has as its key element a filter plate. The filter plate functions as a lens stop for transmitting low frequencies over an effective aperture of a large area and high frequencies over an effective aperture of a small area. For frequencies between the low and high frequencies the filter plate will transmit an increasing frequency through an effective aperture of decreasing area.
In addition to the above there are various phased or spherical array processing and constant beamwidth beam forming techniques used in both underwater acoustics and in air and equally applicable in electromagnetic areas. Unfortunately each of these techniques requires extensive data processing and/or electronics to control and scan the beams formed.